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Conditional execution based on database load (Oracle database)

We have a situation where we have to perform a lengthy query to the database based on human input. As the input changes, the query has to be done over and over again, and the input may change once per second.
The problem is, we know that this will cause a spike in server activity for several seconds, and since it is not critical to have an answer immediately or on every input change, it means we can afford executing or not executing the query.
The criteria we would like to use is the current state of the database server, and only allow the query to be done if it is in a low or medium load state, skipping the query when the database server is under stress.
We use Oracle database for this, and so far we have not found any way, from Java, to do this except by actually loading into the server a known query and benchmark it, but that is essentially adding some load to the server. So my question: is there any other way, specifically in Oracle database, where we can discover from the Java side of the application the load of the database?

Depending on how you define "low or medium load state", I'd guess that hitting v$osstat would give you the information you're after Of course, hitting v$osstat constantly will also add to the load on the server. You may want to write a job that copies the v$osstat data to a table you control periodically (and can thus index appropriately) so that your application can hit that table rather than hitting the dynamic performance view constantly. Depending on the goal (i.e. are you trying to ensure that other users have enough resources or are you trying to ensure that your app remains responsive), you may want to use Resource Manager to control resource utilization among users, you may want to run the query asynchronously from the application, and/or you may want to use some sort of cache at the middle tier to avoid hitting the database every time.

SQL JDBC interceptor for Java that can trace suspicious SQL queries

I am running a Java program with Hibernate. Hibernate generates queries, but we also have some custom DAO queries. Static code analysis/reviews for poorly designed SQL queries is quite hard and resource intensive to do, but they cause real trouble. Is there some JDBC interceptor available, that can warn about sub-par or poorly written SQL queries? I know there are sql monitors such has log4-jdbc, but to my knowledge they do not trace this kind of information at runtime.
By heuristic I mean, that executing a 5s lasting query once a day is ok, but executing 100 of these 5s lasting queries every minute is not ok. Or it could warn about sql queries not containing WHERE statement, which pulls out a large number of rows every time.

Perhaps something like XRebel could solve the issue? You could set thresholds to get notifications if the query is running too long or if too many queries were executed. Plus, you could actually spot N+1 issues just by looking at the results. And the queries are logged with inlined parameters, so you wouldn't have to figure out which parameter is which.

Java Cache Data before entering to database

we have to implement a monitoring module to existing web application. The purpose of the application is to record time taken at each method executed at run time and saving to 2 monitoring tables. As there are many method invocations happening in the application, we can't save to table every time a method is executed.We have used spring aop to intercept time.We used redis to cache data, and in every ten minutes, take the data from cache and save in the database.But redis seems to be a troublesome ideas as it keep making new connections and this give the application a nightmare.Is there any alternative way to do this.We considered about writing to a file and taking data from the file periodically.But that also seemed to be a resource consuming solutions.

I would suggest storing everything in your Java application. If all you want is a few stats, you can keep track of this information in a HashMap and write it every 10 minutes to the database from another thread. Min/Max/Avg time won't take much memory, and you can reset stats once it's written to the database.
If that doesn't suite your needs for some reason, Redis should be fast, and can even help you compute your statistics. I'd setup a connection pool to prevent it from making a new network connection each time. Then, I'd use asynchronous writes (pipelining) in your Redis client to speed up writes. Jedis and JRedis both support this.

How to improve my software project's speed?

I'm doing a school software project with my class mates in Java.
We store the info on a remote db.
When we start the application we pull all the information from the database and transform it into objects to use in our application (using java sql statemens).
In the application we edit some of these objects and then when we exit the application
we save or update information in the database using Hibernate.
As you see we dont use Hibernate for pulling in information, we use it just for saving and updating.
We have 2, but very similar problems.
The loading of object(when we start the app) and the saving of objects(with Hibernate) in the db(when closing the app) is taking too much time.
And our project its not a huge enterprise application, its a quite small app, we just manage some students, teachers, homeworks and tests. So our db is also very very small.
How could we increase performance ?
later edit: if we use a local database it runs very quick, it just runs slow on remote databases

Are you saying you are loading the entire database into memory and then manipulating it? If that is the case, why don't you instead simply use the database as a storage device, and do lookups and manipulation as necessary (using Hibernate if you like, or something else if you don't)? The key there is to make sure that you are using connection pooling, as that will reduce the connection time.
If this is what you are doing, then you could be running into memory issues as well - first, by not caching the entire database in memory, you will reduce memory and will spread out the network load from the beginning/end to the times when it needs to happen.

These 2 sentences are red flags for me :
When we start the application we pull
all the information from the database
and transform it into objects to use
in our application (using java sql
statemens). In the application we edit
some of these objects and then when we
exit the application we save or update
information in the database using
Hibernate.
Is there a requirements reason that you are loading all the information from the database into memory at startup, or why you're waiting until shutdown to save changes back in the database?
If not, I'd suggest a design change. If you've already got Hibernate mappings for the tables in the DB, I'd use Hibernate for both all of your CRUD (create, read, update, delete) operations. And, I'd only load the data that each page in your app needs, as it needs it.
If you can't make that kind of design change at this point, I think you've got to look closely at how you're managing the database connections. Are you using connection pools? Are you opening up multiple connections? Forgetting to release them?
Something else to look at. How are you using Hibernate to save the entities to the db? Are you doing a getHibernateTemplate().get on each one and then doing an entity.save or entity.update on each one? If so, that means you are also causing Hibernate to run a select query for each database object before it does a save or update. So, essentially, you'd be loading each database object twice (once at the beginning of the program, once before saving). To see if that's what's happening, you can turn on the show_sql property or use P6Spy to see exactly what queries Hibernate is running.

For what you are doing, you may very well be better off serializing your objects and writing them out to a flat file.
But, much more likely, you should just read / update objects directly from your database as needed instead of all at once, for all the reasons aperkins gives.
Also, consider what happens if your application crashes? If all of your updates are saved only in memory until the application is closed, everything would be lost if the app closes unexpectedly.

The difference in loading everything from a remote DB server versus loading everything from a local DB server is the network latency / pipe size. The network is a much smaller pipe than anything else. Two questions: first, how much data are we really talking about? Second, what is your network speed? 10/100/1000? Figure between 10 and 20% of your pipe size is going to be overhead due to everything from networking protocols to the actual queries themselves.
As others have stated, the way you've architected is usually high on the list of "don't do". When starting, pull only enough data to initialize the app. As the user works through it, pull what you need for that task.
The ONLY time you pull everything is when they are working in a disconnected state. In that case, you still don't load everything as objects in the application, you just work from a local data store which gets sync'ed with the remote server every so often.

The project its pretty much complete. we cant do large refactoring on it now.
I tried to use a second level cache for Hibernate when saving. EhCacheProvider.
in hibernate.xml:
net.sf.ehcache.hibernate.EhCacheProvider
i have done a config for the cache, ehcache.xml:
i have put the cache.jar in the project build path
and i have set the hibernate property for every class and set in the mapping.
But this cache doesn't seem to have an effect. I dont know if it works(if it is used).

Try minimising number of SQL queries, since every query has its own overhead.
You can enable database compression, which should speed things up when there is a lot of data.
Maybe you are connecting to the database many times?
Check the ping time of remote database server - it might be the problem.

As your application is just slow when running on a remote database server, I'd assume that the performance loss is due to:
Connecting to the server: try to reuse connections (pass the instance around) or use connection pooling
Query round-trip time: use as few queries as possible, see here in case of a hand-written DAL:
Preferred way of retrieving row with multiple relating rows
For hibernate you may use its batch functionality and adjust hibernate.batch_size.
In all cases, especially when you can't refactor larger parts of the codebase, use a profiler (method time or sql queries) to find the bottleneck. I bet you'll find thousands of queries, each taking 10ms RTT) which could be merged into one.

Some other things you can look into:
You can allocate more memory to the JVM
Use the jconsole tool to investigate what the bottlenecks are.

Why dont you have two separate threads?
Thread 1 will load your objects one by one.
Thread 2 will process objects as they are loaded.
Your app will seem more interactive at startup.

It never hurts to review the basics:
Improving speed means reducing time (obviously), and to do that, you find activities that take significant time but can be eliminated or replaced with something that uses less time. What I mean by activity is almost always a function call, method call, or property call, performed on a specific line of code for a specific purpose. If may invoke I/O or it may invoke computation, or both. If its purpose is not essential, then it can be optimized.
Many people use profilers to try to find these time-wasting lines of code, but most profilers miss the target because they look at functions, not lines, they go to sleep during I/O, and they worry about "self time".
Many more people try to guess what could be the problem, or they ask others to guess, such as by asking on SO. Such guesses, in the nature of guesses, are sometimes right - more often not, but people still invest time and resources in them.
There's a very simple way to find out for sure, without guessing, what could fruitfully be optimized, and here is one way to do it in Java.

Thanks for your answers. Their were more than helpful.
We completely solved this problem like so:
Refactored the LOAD code. Now it uses Hibernate with Lazy Fetching.
Refactored the SAVE code. Now it saves, just the data that was modified and right after the time it was modified. This way we dont have a HUGE save an the end.
Im amazed of how good it all went. The amount of new code we had to write was very very small.

Is there a SQL Server profiler similar to Java/.Net profilers?

I love the way I can profile a Java/.Net app to find performance bottlenecks or memory problems. For example, it's very easy to find a performance bottleneck looking at the call tree with execution times and invocation counts per method. In SQL Server, I have stored procedures that call other stored procedures that depend on views, which is similar to Java/.Net methods calling other methods. So it seems the same kind of profiler would be very helpful here. However, I looked far and wide and could not find one. Is anyone aware of such tools, either for SQL Server or any other DBMS?
Update: Thanks fro your replies around SQL Server Profiler, but this tool is very limited. Take a look at the screenshot.

Check out SQL Nexus Tool. This has some good reports on identifying bottlenecks.
SQL Nexus is a tool that helps you identify the root cause of SQL Server performance issues. It loads and analyzes performance data collected by SQLDiag and PSSDiag. It can dramatically reduce the amount of time you spend manually analyzing data.
In one of the Inside SQL 2005 books (maybe T-SQL Querying), there was a cool technique in which the author dumps the SQL profiler output to a table or excel file and applies a pivot to get the output in a similar format as your screenshot.
I have not seen any built-in SQL tools which gives you that kind of analysis.
Another useful post.

In addition to SQL Server Profiler, as mentioned in a comment from #Galwegian, also check out your execution plan when you run a query.
http://www.sql-server-performance.com/tips/query_execution_plan_analysis_p1.aspx
http://en.wikipedia.org/wiki/Query_plan

Another whole thread about the SQL Server profiler:
Identifying SQL Server Performance Problems
I understand what you are talking about, but typically, database optimization takes place at a finer grained level. If the database activity is driven from a client, you should be able to use the existing client profiler to get the total time on each step and then address the low hanging fruit (whether in the database or not).
When you need to profile a particular database step in detail, you can use profiler and a trace.
Typically, the database access has a certain granularity which is addressed on an individual basis and database activity is not linear with all kinds of user access going on, whereas a program profiler is typically profiling a linear path of code.

As mentioned, SQL Server Profiler, which is great for checking what parameters you're program is passing to SQL etc. It won't show you an execution tree though if that's what you need. For that, all I can think of is to use Show Plan to see what exactly is executed at run-time. E.g. if you're calling an sp that calls a view, Profiler will only show you that the sp was executed and what params were passed in.
Also, the Windows Performance Monitor has extensive run-time performance metrics specific to SQL Server. You can run it on the server, or connect remotely.

To find performance bottlenecks, you can use the Database Engine Tuning Advisor (found in Tools menu of SQL Server Management Studio. It provides suggestions for optimizing your queries and offers to optimize them for you automatically (e.x. create the appropriate indexes, etc.).

You could use Sql Profiler - which covers the profiling aspect, but I tend to think of it more as a logging tool.
For diagnosing performance, you should probably just be looking at the query plan.

There's the sql server profiler, but despite it's name, it doesn't do what you want, by the sound of your question. It'll show you a detailed view of all the calls going on in the database. It's Better for troubleshooting the app as a whole, not just one sproc at a time
Sounds like you need to view the execution plan of your queries/spocs in query analyzer and that will give you something akin to the data you are looking for.

As mentioned by several replies the SQL Profiler will show what you're asking for. What you'll have to be sure to do is to turn on the events SP:StmtCompleted, which is in the Stored Procedures group, and if you want the query plans as well turn on Showplan XML Statistics Profile, which is in the Performance group. The XML plan last one gives you a graphical description and shows the actual rows processed by each step in the plan.
If the profiler is slowing your app down, filter it as much as possible and consider going to a server side trace.
HTH
Andy